Stall Control System for Raise Drills and Raise Boring Machines

ABSTRACT

A stall control system for a raise boring machine is provided. In one implementation, the stall control system includes one or more hydraulic control valves connected to thrust cylinders of the raise boring machine to vent pressurize oil from a cap end of the thrust cylinders back to an oil tank or to a rod end of the thrust cylinders. In another implementation, the stall control system includes one or more hydraulic control valves connected to thrust cylinders of the raise boring machine to inject pressurized oil into a rod end of the thrust cylinders to increase pressure on the rod end of the thrust cylinders.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to U.S. Provisional Application No. 63/201,314 filed on Apr. 23, 2021, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The following generally relates to stall control systems and methods for raise drills and raise boring machines.

BACKGROUND

A raise drill or raise boring machine (RBM) 10 is a mechanical device designed to excavate large diameter openings in hard rock. A raise 12 is started by drilling a pilot hole 14 (see FIG. 1 a ) from an upper area 16 to a lower breakthrough area 18 (see FIG. 1 b ). At the breakthrough area 18, the pilot bit 20 is removed and a large diameter reamer 22 is attached (see FIG. 1 c ). The excavation, or opening is called a raise 12 because the large cutter, or reamer 22 is “raised” up from below, pulled back towards the RBM 10 (see FIG. 1 d ). Raises 12 have been completed to a length over 600 m and to a diameter up to 6 m or more.

A raise 12 can be used to supply ventilation to the workings of an underground mine for either fresh air or return (exhaust) air. Raises 12 in smaller diameters can also be used for ore or waste passes that are used to drop blasted mine rock from an upper level to a lower level. Raises 12 can also be used as a travel or escape way for personnel and for installation of mine services such as air lines, water lines or power cables.

The pilot bit 20 and/or reamer 22 is/are attached to the RBM 10 with heavy, high capacity drill rods 24 that are generally 1.52 m in length and with a diameter up to 406.4 mm or greater. The rods 24 have a threaded connection at either end—a male thread at the pin end and a female thread at the box end. The drill rods 24 are hollow to reduce weight and to allow for the flow of water or other fluids to remove cuttings when drilling the pilot hole 14. When reaming, cuttings 26 fall with gravity to the bottom of the hole (see FIG. 1 d ) where they are removed with mobile equipment and disposed of. The drill rods 24 are selected based on the output torque and thrust values of the RBM 10. The output torque is from an electric or hydraulic motor or motors through a multi-stage gear reducer that will reduce the output speed and increase the output torque.

While creating the raise, the RBM 10 is raised and lowered a distance of approximately 2.2 m with a number of hydraulic cylinders 28. The hydraulic cylinders 28 are used with a hydraulic and/or electronic control system 30 to adjust and control the pressure in the hydraulic cylinders 28 for both pilot hole drilling and for reaming the raise 12 to the final diameter.

In operation, an RBM 10 loads the reamer 22 with torque and thrust values that will be close to the torque/tension yield of the drill rods 24. The RBM 10 and drill rods 24 operate at close to full capacity with a margin of safety based on an acceptable level of risk and on the condition of the equipment. Despite their considerable size and weight, the drill rods 24 threaded together in a long string can be modelled as a very large wire rope. With a raise 12 length more than 100 m or so, there is a torsional windup in the drill string 24 before the reamer 22 turns at the bottom of the raise 12 (e.g., as shown in FIG. 1 d ).

The reamer 22 is fitted with formed metal saddles that are used to install a cylindrical or tapered rolling cutter. The cutter is designed with bearings at both ends and with an outer shell equipped with carbide buttons. The carbide buttons can have numerous shapes such as a chisel or wedge and selected to be harder than the rock formation. The saddle layout on the reamer top surface and the placement of carbide buttons on the cutters is to have a spacing in hard rock of approximately 25 mm between adjacent rows. In practice, the thrust loading of the RBM hydraulic cylinders 28 creates tension along the drill string with sufficient force to pull the carbide buttons into the rock formation (see FIG. 1 d ). Micro-fractures develop between the button rows and, when the microfractures meet, a small rock chip falls out of the rock face. When the rock chips fall out, the torque on the reamer 22 drops slightly and the reamer 22 accelerates forward as the thrust value continues to build. As the thrust value builds up on the carbide buttons, the reamer 22 slows to a stop while the micro-fractures develop once again. In practice, the output torque of the RBM 10 and the cutting action is with a rhythmic, load and release cycle and can be seen as a sawtooth waveform. The amplitude and frequency of the machine output torque is determined by the power levels of the machine, the length of the drill string, the type of rock formation and the rotational speed of the drill rods 24.

An RBM 10 is designed to stall in the forward direction of rotation at a fixed value of output torque. This is to protect the gearcase of the RBM 10 as well as the drill string. It is generally not possible to prevent a stall, as there is no way of knowing whether the rock face of the raise could become blocky or even partially collapse, causing the reamer rotation to stop. As a result, every RBM 10 is designed to stall at a maximum forward torque setting. A critical factor is how the developed torsional windup of the drill string due to the machine output torque is relieved. This is done in a slow and controlled fashion for a very good reason. If the reamer 22 is simply lowered from the rock face and allowed to spin ahead from the torsional windup and the rotation of the machine, the uncontrolled reamer rotation can cause a threaded connection to break either at the reamer 22, or with any pin to box threaded connection along the drill string. As a worst case, a broken, unthreaded connection can result in a drop of the reamer 22 and/or sections of the drill string. This can cause extensive and very expensive damage to the reamer 22 and drill string and is considered a catastrophic event with potential damages into millions of dollars, in addition to lost production time.

At a best case, an unthreaded connection as monitored with a pressurized drill string (and indicated with a drop in pressure) results in the need to lower the reamer to the bottom of the raise, removing it from the drill string, and pulling the entire drill string from the hole 14/12. All drill rods 24 are then cleaned and inspected before being properly torqued while being lowered into the hole 14/12 once again. The drill rods 24 reach the bottom of the hole 14/12 where the reamer 22 is attached once again then pulled back up to the rock face so that reaming can continue. The loss of process and production time can be considerable.

As a result, a reamer stall is dealt with in a specific fashion that is typical for all machines, whether manually or electronically controlled.

1. The RBM 10 reaches the maximum output stall torque for a specific time period, generally one or two seconds. With a stall, the drill string and reamer 22 will have come to a full stop.

2. A stall control sequence is activated. This will generally disable the hydraulic control of the cylinders 28 so that the machine operator cannot lower the reamer 22 from the face.

3. The speed command to the main motor and drill string is kept at the value set by the operator or set to a specific fixed value to ensure that rotational power will not be interrupted during the stall routine.

4. The output torque command to the RBM main motor is gradually reduced along with the output speed, either as a single or two separate control values.

5. The intent is to gradually reduce the output torque of the drill rods 24 to the point where the torsional windup of the drill string is greater than the output torque of the RBM 10. This causes a slow and controlled reverse rotation of the drill string and RBM gearcase, relieving the torque on the drill string.

6. Once the output torque reaches a low and safe value, the stall control routine is reset. The machine is operated to lower the reamer 22 from the face. Rotation is started, and the hydraulic cylinders 28 of the RBM 10 are extended to load the reamer 22 once again.

In summary, an RBM 10 is designed to stall, and to stall safely without causing any damage to the RBM 10, drill rods 24 or reamer 22. A stall is dealt with by allowing the torsional windup of the drill string to rotate in reverse to slowly and gradually reduce that torque to a low and safe value.

The stall of an RBM 10 can be stressful for the machine operator, but will not cause any harm to the machine itself as long as the maximum forward torque is properly set. However, with each and every stall of a machine there is a loss of production time. From the initiation of a stall event through to a reset and then application of working load levels once again can take up to 10 full minutes. Two or three stalls in an hour results in a considerable loss of production time. As a result, with poor rock conditions that tend to cause numerous stalls will result in the machine operator running the machine at conservative values that can reduce the potential productivity of the RBM 10 by as much as 30-40%.

In addition to this, as RBMs 10 have increased in size and power, raises can be excavated to a length and diameter once thought not possible. Recent projects are with raise lengths over 600 m and with a diameter of 6 m. With a longer and larger hole 14/12, the time to recover from a stall condition is greater. This is due to the increase in torsional windup along the drill string and the amount of stretch that longer drill string will allow. As holes get longer, stall recovery times increase as well.

SUMMARY

The following provides a stall control system for an RBM 10. Stall control is a mechanism employed to prevent an RBM 10 from stalling by controlling the cap end pressure of the thrust cylinders 28. It is found that stall control (or stall prevention) provides three important advantages for any RBM 10. First, the time lost from a stall event can be addressed. As noted above, time needed to reduce the torsional windup of the drill string, lower the reamer from the face and then to re-apply drill string tension, and begin reaming again can take up to or longer than 10 minutes with a large RBM 10 and a deep hole 14/12. Second, increased machine loading can be achieved. If a stall can be prevented, the RBM 10 can be run at a higher loading of thrust and torque to push further into the installed machine capacity. Third, a higher average machine output can be achieved. If the peak of the output torque sawtooth waveform can be clipped, the overall average machine output will increase considerably, making better use of the installed power available to apply thrust to the reamer 22.

Two configurations are described for providing stall control capabilities in a RBM 10.

In one aspect, there is provided a stall control system for a raise boring machine, the stall control system comprising: one or more hydraulic control valves connected to thrust cylinders of the raise boring machine to vent pressurize oil from a cap end of the thrust cylinders back to an oil tank or to a rod end of the thrust cylinders.

In another aspect, there is provided a stall control system for a raise boring machine, the stall control system comprising: one or more hydraulic control valves connected to thrust cylinders of the raise boring machine to inject pressurized oil into a rod end of the thrust cylinders to increase pressure on the rod end of the thrust cylinders.

In another aspect, there is provided a method of implementing a stall control system for a raise boring machine, the method comprising: connecting one or more hydraulic control valves to thrust cylinders of the raise boring machine; and venting pressurized oil from a cap end of the thrust cylinders back to an oil tank or to a rod end of the thrust cylinders.

In another aspect, there is provided a method for implementing a stall control system for a raise boring machine, the method comprising: connecting one or more hydraulic control valves to thrust cylinders of the raise boring machine; and injecting pressurized oil into a rod end of the thrust cylinders to increase pressure on the rod end of the thrust cylinders.

In other aspects, there are provided computer readable for storing computer executable instructions for implementing such methods.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described with reference to the appended drawings wherein:

FIGS. 1 a-1 d illustrate a raise drilling operation using a RBM 10.

FIG. 2 is a schematic perspective view illustrating a RBM system.

FIG. 3 is a perspective view of a stall control manifold.

FIG. 4 is a hydraulic schematic of a stall control system for a RBM.

DETAILED DESCRIPTION

Referring now to the figures, FIG. 2 illustrates an example of an assembly for a RBM 10 and control system 30, which may also be referred to herein as a “RBM assembly” or “RBM system” interchangeably, understood to include a RBM 10 and any ancillary equipment used to assemble, disassemble and run the RBM 10, including the control system 30 and its components. In this example, the RBM system includes a drill rig assembly 40 that includes the thrust cylinders 28 and operates to drive the pilot bit 10 and reamer 22 by adding or removing drill rods 24 during pilot drilling and reaming operations as discussed above. Also shown are a hydraulic pack assembly 42 that includes the hydraulic control system components and a control console assembly 44 for a rig operator. An electric cabinet assembly 46 contains the electrical components for operating the control system 30 and RBM 10.

Stall Control Factors

RBMs 10 are currently run “open loop”, where an operator will set the reamer speed and thrust cylinder pressure to a certain level of loading. If the thrust pressure is set too high a stall can occur. However, the borderline between a stall occurring or not is the result of a number of dynamic factors and cannot be easily predicted. As a result, many operators reduce the thrust pressure and loading of the RBM 10, knowing that a stall will be less likely. While making the RBM 10 easier and more comfortable to operate it does result in reduced production. On the other hand, a highly skilled operator may push for as much production as possible, constantly adjusting speed and thrust with incremental changes to come as close to a stall as possible and without having too many of them occur. This does result in an increase in production, but with a process that needs to be carefully monitored with constant adjustment and resulting in a more stressful and demanding way of running the RBM 10.

It is recognized that with an effective stall control system, the thrust pressure setting would no longer be critical. The operator could set a desired reamer speed and then a maximum cap end pressure that would be monitored by the machine controller. The machine controller refers to the electronic device that runs the control program and can include any programmable electronic hardware, for example, a programmable logic controller (PLC) or other modular control hardware. That pressure can then be controlled while monitoring the machine output torque and speed, effectively controlling the hydraulic cylinder cap end pressure to prevent a stall.

RBM Pressure Control

Virtually every RBM 10 has the same type of pressure control—manual or electronic volume and pressure control of the oil flow to the cap end of the cylinders 28 when reaming. Oil flow to the cap end to extend the thrust cylinders 28 sets the maximum thrust loading of the cutters on the reamer 22. That thrust loading also determines the amount of torque needed from the gearbox to rotate the drill string at that thrust level.

The hydraulic control circuit of most RBMs 10 is generally with a “meter-in” design, where the flow rate to the cylinders 28 is pressure limited with a T connection to vent oil from an adjustable relief back to tank, in some cases through a flowmeter so the flow rate can be adjusted or monitored. While this does provide an accurate mechanism for setting a desired pressure, if that pressure rises too high, the flow capacity of the control valves does not provide a way to readily drop the cap end thrust pressure.

Once the pressure has developed on the cap end of the cylinders 28, as currently configured, the only practical option is to “drill it away” by allowing the reamer 22 to continue rotating with the feed control in neutral until the cap end pressure drops below the stall threshold. Reducing the thrust pressure by operating the feed directional control valve in the down direction is not considered a feasible option. Lowering the reamer 22 to release that tension can result in a sudden and uncontrolled forward rotation of the reamer 22 that could uncouple a drill rod connection. A loose connection is monitored with the drill string filled with water and pressurized with an air cushion. A drop in pressure indicates a loss of fluid, and that due to a cracked rod or loose threaded connection.

Stall Control System (First Configuration)—Vent Thrust Cylinder Cap End

One solution to prevent a RBM 10 from stalling is with a hydraulic control valve (or valves) that allow for a sudden release or venting of a fixed amount of pressurized oil from the cap end of the RBM thrust cylinders 28. That flow of oil can be directed either back to tank or to the rod end of the cylinders 28. This would be accomplished with additional hardware from that normally installed for the machine pressure control system that is designed for the slow and gradual increase in pressure with a low flow rating and accurate pressure control.

Oil to the cap end of a thrust cylinder 28 causes it to extend, oil to the rod end causes it to retract. When reaming, the cap end is pressurized for a desired thrust value. The rod end of the machine cylinders 28 is returned to the oil tank at the power hydraulic pack 42, generally through a counterbalance or holding valve that will prevent the RBM 10 from dropping in the event of a hose failure. A high volume directional control valve (DCV) with either fixed (on/off) or variable (proportional) action can be installed directly at the RBM 10 and be connected with other valves and outlet ports suitable and designed to provide a positive shut-off when not enabled. For example, the manifold 60 shown in FIG. 3 can be connected such that the inlet port is connected to the cap end of the thrust cylinders 28 and the outlet connected to the rod end of the thrust cylinders 28.

In this configuration, pressure sensors can be installed to detect the pressure of both the cap end and the rod end of the machine thrust cylinders 28. A suitable controller or other electronic device can be used to control the high volume DCV as determined by monitoring the cap and rod end pressure sensors as well as the output torque and rotational speed of the RBM 10. The controller can be programmed to, upon seeing either a rise in machine output torque and/or a decrease in output speed, operate for a fixed time period while monitoring the pressure of the cap and rod end of the RBM 10. An oil flow from the cap end to the rod end would function to lower the thrust pressure as a sudden and controlled event for a specific pressure drop and reduction in machine output torque.

The desired control action is to clip the peak of the output torque sawtooth waveform, keeping it below what is determined to be the stall threshold as measured and detected with the cylinder pressures and machine output torque and speed. The control valve would continue to operate with each and every torque windup cycle, this on average of every few seconds.

It can be appreciated that additional components are needed to prevent that sudden venting of oil from the cap end of the cylinders 28 causing a pressure spike on the rod end of the cylinders 28. A pressure spike can cause stress and degradation of hydraulic components as well as to the flexible hydraulic hoses connecting the machine to the hydraulic power pack assembly 42. The venting of pressurized oil from the cap to rod end of the thrust cylinders 28 is one possible embodiment. Preferably, the venting is installed with a custom manifold directly at the RBM 10 for maximum effectiveness. As noted above, this could include a manifold such as the manifold 60 shown in FIG. 3 , connected as explained above. That is, the custom manifold can be connected to an existing machine according to which valve connections are required and taking into account any safety measures imposed by the system to which it is being connected.

Stall Control System (Second Configuration)—Pressurized Oil to Rod End

With the first configuration, unless the RBM 10 is a new machine build, the first configuration can create some complexity when attempting to retrofit the hardware to an existing machine. The following second configuration can also be used to allow the hardware to be installed with minimal modifications to any RBM 10 directly at the hydraulic power pack assembly 42.

In this example, the system would be installed using the custom hydraulic manifold 60 (see FIG. 3 noted above and described below), which would allow for the installation of the necessary components. Central to the system in this second configuration is again with a PCV, in this case a pressure reducing/relieving valve (or valves), along with additional solenoids and an accumulator designed for high pressure operation. The system would operate when triggered by the machine controller in response to the same conditions as with the first configuration described above, where an increase in torque and a decrease in output speed is seen.

However, in this second configuration, the goal is not to reduce the pressure of the cap end of the cylinders 28 but rather to increase the pressure on the rod end of the cylinders 28. By injecting pressurized oil into the rod end of the cylinders 28, this will create an opposite force that will effectively reduce the machine output thrust but without venting any oil from the cap end of the cylinders 28. Any pressure on the cap end of the cylinders 28 develops an upward force—any pressure on the rod end of the cylinders 28 develops a downward force.

With this approach, the pressure developed in the cap end of the cylinders 28 is maintained, and no time is needed to recover after having vented oil from the cap end either to tank or to the rod end of the cylinders 28. The hydraulic thrust cylinders 28, with the cap end pressurized to a level needed for a “working load” can have their total thrust output modified with that pressure injection into the cylinder rod end(s). Moreover, the pressure injection into the rod end of the cylinders 28 results in an immediate and more responsive control as opposed to venting oil, and then needing to recover from that system upset.

Referring now to FIG. 3 , an example of the stall control manifold 60 is shown. The manifold 60 includes a PCV 62 a for providing stall prevention pressure control as described below, and can also include a second PCV 62 b to be used if more flow is required. Also shown in FIG. 3 are a stall prevention solenoid 66 which is energized to activate the stall control and allow a flow of oil from the accumulator 63 (see FIG. 4 ) to the machine thrust cylinder rod ends as described below. The manifold 60 also includes an accumulator charge 64 to activate the accumulator 63.

A potential stall condition can be monitored with a machine's existing processor with calculation and display of:

a) Output torque with values from either pressure sensors for a hydraulic drive, current sensors for an electric drive or values provided from an electric drive electronic controller,

b) Output speed with drive motor or drive head RPM sensor and gearbox ratios,

c) Bit force (net thrust) with thrust cylinder cap and rod end pressure sensors, and

d) Machine extended height with a draw-wire sensor (optional).

An impending stall can be detected based on empirical data from field testing and can apply a formula that will state:

IF (Drive RPM drops by 0.XX) AND (Bit Force increases by XXXX) OR (Output Torque increases by XXXX) THEN Activate Stall Control.

As indicated above, stall control can function in one of two ways. In one implementation, this stall control function can be performed by venting oil from the cap to the rod end of the thrust cylinders 28 with a manifold 60 installed at the thrust cylinders 28 of the RBM 10. In a second implementation, this stall control function can be performed by injecting pressurized oil stored in an accumulator in a controlled fashion to the rod end of the thrust cylinders 28 with a manifold 60 installed at the hydraulic power pack assembly 42 of the RBM 10.

The following will provide an example using the second implementation, referring to FIG. 4 . With the second implementation there are fewer variables to contend with than the first implementation, thus increasing the predictability and repeatability of the process.

With the hydraulic pumps 70 of the RBM 10 in operation, and the drive head rotating, the system is enabled by setting a feed joystick in the control console 44 to the “Up” position.

This sends a signal to the proportional coil (A) of directional control valve 78. The directional control valve 78 will allow a flow of oil from the feed pump 70 to the cap end of the four thrust cylinders 28. The directional control valve 78 will set the feed volume based on the setting of the control console feed volume potentiometer.

Simultaneous with the operation of the directional control valve 78 a solenoid (not shown) is energized. Such a solenoid connects the return oil from the rod end of the thrust cylinders 28 to tank to ensure there is no return back pressure.

Simultaneous with the operation of the directional control valve 78, another solenoid (not shown) is energized. This solenoid makes a T connection from the directional control valve 78 oil flow to the proportional relief valve 80. The proportional relief valve 80 will set the maximum system pressure based on the setting of the control console feed pressure potentiometer.

Simultaneous with the operation of the directional control valve 78, solenoid 81 is energized. Solenoid 81 connects the feed pump flow of oil from the directional control valve 78 through solenoid 81 back to a feed pump unloading valve (not shown). The pump 70 goes from a standby pressure of, for example, 290 psi (20 bar) to a possible maximum of, for example, 3,200 psi (220 bar).

The system continues to function with the operator free to adjust the feed volume with the directional control valve 78 and the feed pressure with the proportional relief valve 80. The amount of oil being returned to tank through the relief valve 80 is monitored and displayed with a flowmeter 72.

An impending stall is detected with a slowing of the machine drive head rotation, an increase in bit force developed from the thrust cylinders and the output torque of the machine. A control program running a calculation with set trigger points will decide when to trigger the stall control function. When a stall control is triggered, the solenoid connecting the return oil from the rod end to tank, is de-energized. This is to prevent the oil on the rod end of the cylinders 28 from returning to tank.

Simultaneous with the operation of this solenoid, solenoid 66 is energized. Solenoid 66 allows a flow of oil from a charged accumulator 63 through one or two proportional pressure reducing/relieving valves 62 a and 62 b.

A 0-10 VDC signal from the machine processor or controller can be used to set the maximum pressure of the oil from the accumulator 63 to the rod end of the machine thrust cylinders 28. The maximum pressure available will be the pressure that was stored in the accumulator 63.

The flow of oil from the accumulator 63 to the rod end of the cylinders 28 develops a downward force to a value determined by the maximum pressure allowed through valves 62 a and 62 b. This can be done using a basic formula of thrust cylinder total rod end square inch area×pressure=force.

The pressure of the oil that is allowed to flow from the accumulator 63 to the thrust cylinder rod ends develops a downward force. That downward force directly counteracts the upward force developed on the cap end of the thrust cylinders 28, in order to reduce the upward force.

It may be noted that the settings of the proportional pressure reducing/relieving valves 62 a, 62 b, as set with a 0-10 VDC signal, can remain in a steady state, and do not have to be cycled up/down or on/off. This is because while the command signal will set the maximum pressure allowed to flow to the cylinder rod ends, no flow is possible unless solenoid 66 is energized.

It may also be noted that two valves (i.e., 62 a and 62 b) are used, but only one may be needed. If the flow of oil from one valve 62 a/ 62 b is sufficient to develop the needed pressure at the thrust cylinder rod ends, then the other can be placed on standby and without a command signal. If two valves are needed at all times, they could both be replaced with a single valve 62, having a higher flow rating.

Solenoid 66 is the only device that needs to be energized to operate the stall control function, along with ensuring that the solenoid connecting the return oil from the rod end to tank is de-energized at the same time. Once the system has functioned as needed, solenoid 66 is de-energized and the solenoid S3A connecting the return oil from the rod end to tank is energized.

It is expected that with a high thrust load, the raise drill will operate with an output torque close to the maximum allowable forward run limit where a stall will occur. The output torque of any raise drill is cyclical based on the cutting action of the reamer 22, with the output torque seen as a sawtooth waveform.

The stall control function operates to clip the peak of every cycle of the output torque sawtooth waveform. This will reduce the amplitude of the output torque and allow for a higher average machine loading as the torque output will be more consistent. The frequency of the output torque will vary based on reamer size, ground conditions, machine capacity etc., but is generally with a full cycle every 5 to 10 seconds.

The accumulator 63 that stores the oil needed to operate the stall control function can be charged from virtually any pump that has a flow and pressure rating to suit the dynamics and the duty cycle of stall control. For example, this can be done with a small tooling pump used to operate convenience and auxiliary functions that can vary with each machine. The pump is a piston type with an unloading valve, much as with the feed pump 70. The tooling pump is shifted from a standby to run pressure with a recharge solenoid (e.g., with solenoid 64). With the recharge solenoid energized, oil is allowed to flow from the pump to the stall control manifold 60.

At the stall control manifold, solenoid 64 is energized to allow oil from the tooling pump to charge the accumulator 63. The pressure of the oil to the accumulator 63 is monitored with a pressure transducer 65. The pressure transducer 65 sends a 4-20 mA signal to the controller or processor so that the maximum pressure is known.

The controller or processor will de-energize solenoid 64 when the accumulator 63 has charged to the desired pressure value. Once the accumulator 63 has charged, both solenoid 64 and the recharge solenoid are de-energized.

It may be noted that charging of the accumulator 63 needs to be done when the system is not in use for stall control, when solenoid 66 is energized and in use. Charging of the accumulator 63 is sequenced by the controller or processor when stall control is not active.

For simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the examples described herein. However, it will be understood by those of ordinary skill in the art that the examples described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the examples described herein. Also, the description is not to be considered as limiting the scope of the examples described herein.

It will be appreciated that the examples and corresponding diagrams used herein are for illustrative purposes only. Different configurations and terminology can be used without departing from the principles expressed herein. For instance, components and modules can be added, deleted, modified, or arranged with differing connections without departing from these principles.

It will also be appreciated that any module or component exemplified herein that executes instructions may include or otherwise have access to computer readable media such as storage media, computer storage media, or data storage devices (removable and/or non-removable) such as, for example, magnetic disks, optical disks, or tape. Computer storage media may include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. Examples of computer storage media include RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by an application, module, or both. Any such computer storage media may be part of the controller or control system, any component of or related thereto, etc., or accessible or connectable thereto. Any application or module herein described may be implemented using computer readable/executable instructions that may be stored or otherwise held by such computer readable media.

The steps or operations in the flow charts and diagrams described herein are just for example. There may be many variations to these steps or operations without departing from the principles discussed above. For instance, the steps may be performed in a differing order, or steps may be added, deleted, or modified.

Although the above principles have been described with reference to certain specific examples, various modifications thereof will be apparent to those skilled in the art as outlined in the appended claims. 

1. A stall control system for a raise boring machine, the stall control system comprising: one or more hydraulic control valves connected to thrust cylinders of the raise boring machine to vent pressurized oil from a cap end of the thrust cylinders back to an oil tank or to a rod end of the thrust cylinders.
 2. The system of claim 1, further comprising pressure sensors coupled to the thrust cylinders to detect the pressure of the cap end and the rod end of the thrust cylinders.
 3. The system of claim 2, further comprising a controller coupled to the pressure sensors to monitor the pressure at the cap end and the rod end of the thrust cylinders.
 4. The system of claim 3, wherein the controller is programmed to, upon seeing either a rise in output torque of the raise boring machine, a decrease in output speed of the raise boring machine, or both; operate the system for a fixed time period while monitoring the pressure of the cap end and the rod end of the thrust cylinders.
 5. The system of claim 1, wherein the hydraulic control valves are high volume directional control valves.
 6. The system of claim 1, wherein the venting is provided by a manifold installed directly at the raise boring machine.
 7. A method of implementing a stall control system for a raise boring machine, the method comprising: connecting one or more hydraulic control valves to thrust cylinders of the raise boring machine; and venting pressurized oil from a cap end of the thrust cylinders back to an oil tank or to a rod end of the thrust cylinders.
 8. The method of claim 7, further comprising coupling pressure sensors to the thrust cylinders and detecting the pressure of the cap end and the rod end of the thrust cylinders.
 9. The method of claim 8, further comprising coupling a controller to the pressure sensors and monitoring the pressure at the cap end and the rod end of the thrust cylinders.
 10. The method of claim 9, wherein the controller is programmed to, upon seeing either a rise in output torque of the raise boring machine, a decrease in output speed of the raise boring machine, or both; operate the system for a fixed time period while monitoring the pressure of the cap end and the rod end of the thrust cylinders.
 11. The method of claim 7, further comprising installing a manifold directly at the raise boring machine to perform the venting.
 12. A stall control system for a raise boring machine, the stall control system comprising: one or more hydraulic control valves connected to thrust cylinders of the raise boring machine to inject pressurized oil into a rod end of the thrust cylinders to increase pressure on the rod end of the thrust cylinders.
 13. The system of claim 12, further comprising a manifold installed at a hydraulic power pack for the raise boring machine.
 14. The system of claim 13, wherein the manifold comprises the one or more hydraulic control valves and one or more solenoids and is coupled to an accumulator configured for high pressure operation.
 15. The system of claim 14, wherein the oil injected into the rod end of the thrust cylinders is stored in the accumulator.
 16. The system of claim 15, wherein the accumulator is charged only when the system is not in use for a stall control operation.
 17. The system of claim 12, further comprising pressure sensors coupled to the thrust cylinders to detect the pressure of the cap end and the rod end of the thrust cylinders.
 18. The system of claim 17, further comprising a controller coupled to the pressure sensors to monitor the pressure at the cap end and the rod end of the thrust cylinders.
 19. The system of claim 18, wherein the controller is programmed to, upon seeing either a rise in output torque of the raise boring machine, a decrease in output speed of the raise boring machine, or both; operate the system for a fixed time period while monitoring the pressure of the cap end and the rod end of the thrust cylinders.
 20. The system of claim 12, wherein the one or more hydraulic control valves are pressure relief valves.
 21. A method for implementing a stall control system for a raise boring machine, the method comprising: connecting one or more hydraulic control valves to thrust cylinders of the raise boring machine; and injecting pressurized oil into a rod end of the thrust cylinders to increase pressure on the rod end of the thrust cylinders.
 22. The method of claim 21, further comprising installing a manifold at a hydraulic power pack for the raise boring machine.
 23. The method of claim 22, wherein the manifold comprises the one or more hydraulic control valves and one or more solenoids and is coupled to an accumulator configured for high pressure operation.
 24. The system of claim 23, further comprising storing the oil injected into the rod end of the thrust cylinders in the accumulator.
 25. The method of claim 24, wherein the accumulator is charged only when the system is not in use for a stall control operation.
 26. The method of claim 21, further comprising coupling pressure sensors to the thrust cylinders and detecting the pressure of the cap end and the rod end of the thrust cylinders.
 27. The method of claim 26, further comprising coupling a controller to the pressure sensors and monitoring the pressure at the cap end and the rod end of the thrust cylinders.
 28. The method of claim 27, wherein the controller is programmed to, upon seeing either a rise in output torque of the raise boring machine, a decrease in output speed of the raise boring machine, or both; operate the system for a fixed time period while monitoring the pressure of the cap end and the rod end of the thrust cylinders. 